In connection with various types of chemical delignification, it is decisively important to obtain persistently uniform and proportional admixing of chemicals with the pulp in order to achieve acceptable results. With such uniform admixing it is then possible to obtain uniform results in terms of treatment, as well as optimum utilization of the chemicals to the smallest required extent, as well as the lowest required temperature and shortest required reaction time. In order to minimize the chemical demand, and to further reduce the energy demand, it is desirable to carry out this treatment at a relatively high pulp concentration, preferably from about 10 to 25%.
In connection with the known devices, however, such high pulp concentrations create problems of a uniform distribution of the chemicals in the pulp. Present such devices normally comprise rotary members, which intensively agitate the pulp while the chemicals are simultaneously added thereto. Presently available devices are also relatively large, and require a great deal of energy. A substantial portion of the energy supplied to these devices is transformed solely into heat, and is thus not utilized efficiently during the mixing operation itself.